ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 471 



slightly enlarged outwards. The membrane only contains very little 

 cellulose matter, but is richer in pectic substances. The ccenobia are 

 more or less ellipsoidal or subglobose. The papillate pole always points 

 backwards during movement. They measure when adult 170 x 140^.. 

 As regards the division and orientation of the cells in the ccenobium, 

 the author finds that the position occupied by the five rings of cells 

 after the first cross-division has taken place, remains always the same. 

 Tlie envelopes of the ccenobium present the same structural characters as 

 those indicated for Volvox globator. Very fine intercellular communica- 

 tions occur. The author describes the natation of Eudorina, and adds 

 some general considerations on the Volvocacea?. 



Cytology of the Chroococcaceae.* — Elizabeth Acton gives an account 

 of her observations on the cytology of the Chroococcacese. In sum- 

 marizing her results she says that : — 1. In the Chroococcaceas a highly 

 specialized nucleus does not occur. 2. A gradual transition in cell- 

 structure is found, from almost undifferentiated in the lower types to a 

 somewhat specialized one in the highest {Chroococcus macrocarpus). 

 3. The protoplast consists of a ground substance traversed by a reticulum 

 of delicate threads, with nodal thickenings, which are " plasmatic 

 microsomes " — stores of reserve materials elaborated by the pigmented 

 parts of the protoplast. 4. In most species there is no definite demar- 

 cation of central and peripheral regions, but the inner microsomes 

 (" centralkorner " of Kohl) accumulate metachromatic and the outer 

 accumulate cyanophycin. 5. C. turgidus is of this type, but with some 

 differences. 6. In it the number of metachromatin granules varies 

 greatly in different specimens. If there be much metachromatin, it 

 diffuses into the ground substance, and a period of active division takes 

 place. At this time the microsomes of the central region react only 

 with cytoplasmic stains. 7. Division occurs by the constriction of the 

 cell into two halves. The central reticulum may now stain a little more 

 intensely, and the threads tend to be drawn out parallel, but the cross- 

 connexions are still visible. 8. Metachromatin may represent a stage in 

 the formation of chromatin. 9. In Glceocapsa a deep staining of the 

 central reticulum is often shown, simulating Olive's " spireme " stage. 

 This may be an advance in specialization of the central region, or 

 more probably an artefact. 10. In Merismopedia elegans, a higher type, 

 there is a definite " central body " or " nucleus " at the time of division. 

 This is not a nucleus of the higher-plant type, but simply an accumula- 

 tion of chromatin, etc., at nodal points in a small central region. This 

 " nucleus " seems to disperse itself along the reticulum after division. 

 Divison of the " nucleus " takes place before it is reached by the in- 

 growing cell-wall. 11. Chroococcus macrococcus represents the highest 

 type found by the author. It has a definite " nucleus " and cytoplasm. 

 Only the peripheral portion of the " nucleus " stains deeply with 

 chromatin stains, and contains a fine reticulum with chromatin at the 

 nodal points. The interior of the " nucleus " is probably a sap-vacuole. 

 The cytoplasm contains sap-vacuoles, and hence appears coarsely reticu- 

 late ; but the fine reticulum is also present, though distorted. The 



* Ann. of Bot., xxviii. (1914) pp. 433-54 (2 pis.). 



